Apparatuses and methods for handovers between heterogeneous networks

ABSTRACT

A mobile communication device is provided with a plurality of processing logic units. A first processing logic unit is configured to connect the mobile communication device to a first wireless network for wireless transceiving via a first link. A second processing logic unit is configured to determine whether a second link to a second wireless network is available in response to detecting a low performance condition of the first link. Particularly, the first wireless network and the second wireless network are heterogeneous networks. A third processing logic unit is configured to hand over the mobile communication device from the first wireless network to the second wireless network in response to a transceiving rate of the second link being greater than a first value.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims priority of U.S. Provisional Application No.61/522,045, filed on Aug. 10, 2011, and the entirety of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to handovers in the field of wirelesscommunications, and more particularly, to apparatuses and methods forhandovers between heterogeneous networks to improve the performance ofwireless transceiving.

2. Description of the Related Art

With growing demand for ubiquitous computing and networking, variouswireless technologies have been developed, such as the Wireless Fidelity(WiFi) technology, Global System for Mobile communications (GSM)technology, General Packet Radio Service (GPRS) technology, EnhancedData rates for Global Evolution (EDGE) technology, Wideband CodeDivision Multiple Access (WCDMA) technology, Code Division MultipleAccess 2000 (CDMA-2000) technology, Time Division-Synchronous CodeDivision Multiple Access (TD-SCDMA) technology, WorldwideInteroperability for Microwave Access (WiMAX) technology, Long TermEvolution (LTE) technology, Time-Division LTE (TD-LTE) technology, andothers. For user convenience and flexibility, most Mobile Stations (MSs)nowadays are equipped with more than one wireless communication modulefor supporting different wireless technologies. However, each wirelesstechnology has its own features, such as bandwidth, average coverage,and service rate, etc. Particularly, the bandwidth and coverage providedto an MS by a wireless network may vary according to the locationconditions of the MS and/or the time condition.

Take an MS operating in either an Android or a Windows system, whichsupports WiFi and WCDMA technologies, for example. The MS always selectsa WiFi network over a WCDMA network, even if the signal quality of theWiFi network is bad while the signal quality of the WCDMA network isfair/good. That is, the MS is configured to stay connected with the WiFinetwork with bad signal quality, regardless of the availability of theWCDMA network with fair/good signal quality. In such circumstances, evenbrowsing a web page may take a long time, and accordingly, the user mayexperience a serious delay of wireless connectivity. Thus, to improvethe performance of wireless transceiving, it is desirable to providesmart handovers between heterogeneous networks.

BRIEF SUMMARY OF THE INVENTION

In one aspect of the invention, a mobile communication device isprovided. The mobile communication device comprises a first processinglogic unit, a second processing logic unit, and a third processing logicunit. The first processing logic unit is configured to connect themobile communication device to a first wireless network for wirelesstransceiving via a first link. The second processing logic unit isconfigured to determine whether a second link to a second wirelessnetwork is available in response to detecting a low performancecondition of the first link, wherein the first wireless network and thesecond wireless network are heterogeneous networks. The third processinglogic unit is configured to hand over the mobile communication devicefrom the first wireless network to the second wireless network inresponse to a transceiving rate of the second link being greater than afirst value.

In another aspect of the invention, a method for a mobile communicationdevice to handover between a plurality of heterogeneous networks isprovided. The method comprises the steps of connecting to a firstwireless network for wireless transceiving via a first link, determiningwhether a second link to a second wireless network is available inresponse to detecting a low performance condition of the first link,wherein the first wireless network and the second wireless network areheterogeneous networks, and handing over the mobile communication devicefrom the first wireless network to the second wireless network inresponse to a transceiving rate of the second link being greater than afirst value.

In yet another aspect of the invention, a mobile communication device isprovided. The mobile communication device comprises a first processinglogic unit, a second processing logic unit, a third processing logicunit, and a fourth processing logic unit. The first processing logicunit is configured to connect the mobile communication device to a firstwireless network for wireless transceiving via a first link. The secondprocessing logic unit is configured to scan for a nearby second wirelessnetwork with a current signal quality, wherein the first wirelessnetwork and the second wireless network are heterogeneous networks. Thethird processing logic unit is configured to apply a condition check onthe current signal quality of the second wireless network according to aresult of whether the mobile communication device was previouslyconnected to the second wireless network prior to being connected to thefirst wireless network. The fourth processing logic unit is configuredto hand over the mobile communication device from the first wirelessnetwork to the second wireless network in response to passing of thecondition check.

In still another aspect of the invention, a method for a mobilecommunication device to handover between a plurality of heterogeneousnetworks is provided. The method comprises the steps of connecting to afirst wireless network for wireless transceiving via a first link,scanning for a nearby second wireless network with a current signalquality, wherein the first wireless network and the second wirelessnetwork are heterogeneous networks, applying a condition check on thecurrent signal quality of the second wireless network according to aresult of whether the mobile communication device was previouslyconnected to the second wireless network prior to being connected to thefirst wireless network, and handing over the mobile communication devicefrom the first wireless network to the second wireless network inresponse to passing of the condition check.

Other aspects and features of the present invention will become apparentto those with ordinarily skill in the art upon review of the followingdescriptions of specific embodiments of the mobile communication devicesand the methods for a mobile communication device operating as an MS tohandover between a plurality of heterogeneous networks.

BRIEF DESCRIPTION OF DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 is a block diagram of a wireless communications environmentaccording to an embodiment of the invention;

FIG. 2 is a block diagram illustrating an exemplary softwarearchitecture of the mobile communication device 110 according to anembodiment of the invention;

FIG. 3 is a block diagram illustrating an exemplary softwarearchitecture of the mobile communication device 110 according to anotherembodiment of the invention;

FIG. 4 is a state transition diagram illustrating state machineoperations of the mobile communication device 110 according to anembodiment of the invention;

FIG. 5 is a schematic diagram illustrating the ping-pong effect for themobile communication device 110 wandering around the coverage edge ofthe WLAN 130 and the coverage of the cellular network 120;

FIG. 6 is a flow chart illustrating a smart handover method for handingover the mobile communication device 110 from the cellular network 120to the WLAN 130 according to an embodiment of the invention;

FIG. 7 is a curve diagram illustrating a 2-stage monitoring for thesignal quality of nearby WLANs according to an embodiment of theinvention;

FIG. 8A is a schematic diagram illustrating RSSI changes for inwardmovement towards a WLAN according to an embodiment of the invention;

FIG. 8B is a schematic diagram illustrating RSSI changes for outwardmovement from a WLAN according to an embodiment of the invention;

FIG. 9 is a flow chart illustrating a smart handover method for handingover the mobile communication device 110 from the WLAN 130 to thecellular network 120 according to an embodiment of the invention; and

FIG. 10 is a curve diagram illustrating a 2-stage monitoring for thesignal quality of nearby WLANs according to another embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. It should be understood that the embodimentsmay be realized in software, hardware, firmware, or any combinationthereof.

FIG. 1 is a block diagram of a wireless communications environmentaccording to an embodiment of the invention. The wireless communicationsenvironment 100 comprises a mobile communication device 110, a cellularnetwork 120 and a non-cellular network 130. The mobile communicationdevice 110 may selectively connect to one or both of the cellularnetwork 120 and the non-cellular network 130 for obtaining wirelessservices. The cellular network 120 may be a GSM system, GPRS system,WCDMA system, CDMA-2000 system, TD-SCDMA system, WiMAX system, LTEsystem, or TD-LTE system, etc., depending on the Radio Access Technology(RAT) in use. The cellular network 120 comprises at least one cellularstation 121 (or so-called base station or access station), at least onecontrol node 122, and a core network 123, wherein the cellular station121 is controlled by the control node 122 to provide the functionalityof wireless transceiving for the cellular network 120, and the cellularstation 121 and the control node 122 together may be referred to as aradio access network or access network. For example, if the cellularnetwork 120 is a WCDMA system, the cellular station 121 may be a NodeB,the control node 122 may be a Radio Network Controller (RNC), and thecore network 123 may be a General Packet Radio Service (GPRS) core whichincludes a Home Location Register (HLR), at least one Serving GPRSSupport Node (SGSN), and at least one Gateway GPRS Support Node (GGSN).Alternatively, the cellular network 120 may not comprise any controlnode. For example, if the cellular network 120 is an LTE system, thecellular station 121 may be an Evolved-NodeB (E-NodeB), and the corenetwork 123 may be an Evolved Packet Core (EPC) which includes a HomeSubscriber Server (HSS), Mobility Management Entity (MME), ServingGateway (S-GW), and Packet Data Network Gateway (PDN-GW or P-GW).

The non-cellular network 130 may be a Wireless Local Area Network(WLAN), a Bluetooth Personal Area Network (BT PAN), ZigBee Wireless PAN(ZigBee WPAN), or others, implemented as an extension of wired localarea networks and may be able to provide the last few meters ofconnectivity between a wired network and mobile or fixed devices. Asshown in FIG. 1, the non-cellular network 130, which is illustrated as aWLAN for example, is established by an Access Point (AP) 131 which mayconnect to a local area network by an Ethernet cable. The AP 131typically receives, buffers, and transmits data between the WLAN and thewired network infrastructure. The AP 131 may have, on average, acoverage varying from 20 meters in an area with obstacles (walls,stairways, elevators etc) to 100 meters in an area with clear line ofsight. Note that, in the following description, the WLAN is only givenas an example, and the invention is not limited thereto. Alternatively,the non-cellular network 130 may be a BT PAN, ZigBee WPAN, or others.

The mobile communication device 110 may also be referred to as a MobileStation (MS), Mobile Terminal (MT), or User Equipment (UE). For example,the mobile communication device 110 may be a mobile phone (also known asa cellular or cell phone), a smart phone, a laptop computer withwireless communications capability, or others. The mobile communicationdevice 110 may comprise two wireless modules (not shown) for performingthe functionality of wireless transceiving to and from the cellularnetwork 120 and the non-cellular network 130. To further clarify, eachwireless module may comprise a Baseband unit (not shown) and a RadioFrequency (RF) unit (not shown). The Baseband unit may contain multiplehardware devices to perform baseband signal processing, including analogto digital conversion (ADC)/digital to analog conversion (DAC), gainadjusting, modulation/demodulation, encoding/decoding, and so on. The RFunit may receive RF wireless signals, convert the received RF wirelesssignals to baseband signals, which are processed by the Baseband unit,or receive baseband signals from the Baseband unit and convert thereceived baseband signals to RF wireless signals, which are latertransmitted. The RF unit may also contain multiple hardware devices toperform radio frequency conversion. For example, the RF unit maycomprise a mixer to multiply the baseband signals with a carrieroscillated in the radio frequency of the wireless communications system,wherein the radio frequency may be 2.4 GHz utilized in WiFi systems, or900 MHz, 1900 MHz, or 2100 MHz utilized in WCDMA systems, or may be 900MHz, 2100 MHz, or 2.6 GHz utilized in LTE systems, or others dependingon the RAT in use. Also, the mobile communication device 110 maycomprise a controller module (not shown) for controlling the operationof the two wireless modules and other functional components, such as adisplay unit and/or keypad serving as a Man-Machine Interface (MMI), astorage unit storing the program codes of applications, or others.Alternatively, the two wireless modules may negotiate with each otherfor coordinating the respective operations thereof, without anymediator, e.g., the controller module.

FIG. 2 is a block diagram illustrating an exemplary softwarearchitecture of the mobile communication device 110 according to anembodiment of the invention. In the exemplary software architecture, twoprotocol stack handlers 10 and 20, each of which may be implemented asprogram code, when loaded and executed by a processing unit orMicro-Processing Unit (MCU) (e.g., an MCU of a Baseband unit) with aplurality of processing logic units, are configured to communicate withthe cellular network 120 and the non-cellular network 130, respectively,in compliance with a respective wireless communication protocol. Also,the exemplary software architecture includes an mediator 30 which may beimplemented as program code and when loaded and executed by a processingunit or MCU with a plurality of processing logic units, is configured tocontrol/coordinate the operations of the protocol stack handler 10 and20 to practice the smart handover method of the invention.Alternatively, in another embodiment as shown in FIG. 3, the protocolstack handler 10 and 20 may directly negotiate with each other forcoordinating the respective operations thereof to practice the smarthandover method of the invention, without the mediator 30.

Specifically, the mobile communication device 110 is capable ofperforming smart handovers between the cellular network 120 and thenon-cellular network 130 for obtaining wireless services with fairtransceiving rates. FIG. 4 is a state transition diagram illustratingstate machine operations of the mobile communication device 110according to an embodiment of the invention. The “Cellular-connected”state represents a state where the mobile communication device 110 isconnected to the cellular network 120 for obtaining wireless services,while the “WiFi-associated” state represents a state where the mobilecommunication device 110 is connected to the non-cellular network 130for obtaining wireless services. For the case where the mobilecommunication device 110 is in the “Cellular-connected” state, if a newAP is detected with a signal quality greater than a threshold value, themobile communication device 110 may disconnect with the cellular network120 and connect to the non-cellular network 130 via the new AP, and thenenter the “WiFi-associated” state. In one embodiment, the signal qualityof the AP may be determined by measuring the Received Signal StrengthIndicator (RSSI) of the signals from the AP. Note that, other measuringindicators, such as Signal to Noise Ratio (SNR), Interference to SignalRatio (ISR), Packet Error Rate (PER), and Bit Error Rate (BER), etc.,may be employed for determining the signal quality of an AP, and theinvention is not limited thereto. In another situation, if the signalquality of a previously detected AP increases so that the currentlydetected signal quality is greater than the sum of the previouslydetected signal quality and a margin value, the mobile communicationdevice 110 may disconnect with the cellular network 120 and connect tothe non-cellular network 130 via the AP, and then enter the“WiFi-associated” state. To further clarify, the margin value may be apredetermined buffer to eliminate the ping-pong effect as shown in FIG.5. Particularly, the ping-pong effect occurs when the coverage of thecellular network 120 and the non-cellular network 130 overlap and themobile communication device 110 wanders near the coverage edge of thenon-cellular network 130. Around the coverage edge, the signal qualityof the non-cellular network 130 may be weak and unstable, and withoutthe margin value, handovers back and forth between the cellular network120 and the non-cellular network 130 may be too frequent, thus consumingunnecessary power. Thus, by configuring a proper margin value, frequenthandovers between the cellular network 120 and the non-cellular network130 may be avoided. For the case where the mobile communication device110 is in the “WiFi-associated” state, if the transceiving rate(referred to herein as “speed” for brevity) of the link to the currentlyassociated AP is lower than the speed of the link to the cellularnetwork 120, the mobile communication device 110 may disconnect with thenon-cellular network 130 and connect to the cellular network 120, andthen enter the “Cellular-connected” state. To be more specific, thespeed of the link to the currently associated AP may be determinedaccording to the transceiving status between the mobile communicationdevice 110 and the associated AP, and the speed of the link to thecellular network 120 may be determined according to the systeminformation broadcasted by the cellular network 120. In anotherembodiment, the mobile communication device 110 may transit from the“WiFi-associated” state to the “Cellular-connected” state if the speedof the link to the currently associated AP is lower than a predeterminedvalue (e.g., 2 Mbps).

FIG. 6 is a flow chart illustrating a smart handover method for handingover the mobile communication device 110 from the cellular network 120to the non-cellular network 130 according to an embodiment of theinvention. In this embodiment, the mobile communication device 110 isinitially connected to the cellular network 120 and is in a“Cellular-connected” state. To begin, the mobile communication device110 periodically scans for any nearby non-cellular network (step S610).If a non-cellular network is detected, the mobile communication device110 then determines whether it was previously connected to the detectednon-cellular network (step S620). If so, the mobile communication device110 further determines whether the currently detected signal quality ofthe non-cellular network is greater than the sum of the previouslydetected signal quality of the non-cellular network and a margin valueto eliminate the ping-pong effect (step S630). Specifically, the mobilecommunication device 110 may distinguish a new non-cellular network froma previously associated non-cellular network by identifying the MediaAccess Control (MAC) addresses and/or Service Set Identifiers (SSIDs) ofall detected non-cellular networks. That is, if the MAC address or SSIDof a detected non-cellular network is not found in the connectionhistory stored in the mobile communication device 110, then the detectednon-cellular network is a new non-cellular network; otherwise, thedetected non-cellular network is a previously associated non-cellularnetwork. It is noted that, there may be a situation where two or morenon-cellular networks in an area are configured with the same SSID, andin this case, the MAC address instead of the SSIDs should be used touniquely identify each one of the non-cellular networks in the area. Thepreviously detected signal quality of the non-cellular network may bethe signal quality of the non-cellular network at the time when themobile communication device 110 decided to perform handover from thenon-cellular network to the cellular network 120. If the currentlydetected signal quality of the non-cellular network is greater than thesum of the previously detected signal quality of the non-cellularnetwork and a margin value to eliminate the ping-pong effect, the mobilecommunication device 110 conducts handover to the non-cellular network.Specifically, the mobile communication device 110 first tries toestablish a connection to the non-cellular network (step S640), and thenwaits for acceptance of the connection from the non-cellular network(step S650). If the connection is accepted by the non-cellular network,the mobile communication device 110 then disconnects with the cellularnetwork 120 (step S660) and enters the “WiFi-associated” state;otherwise, if the connection is rejected by the non-cellular network,the mobile communication device 110 stays in the “Cellular-connected”state. Subsequent to step S620, if not, i.e., the detected non-cellularnetwork is a new non-cellular network which the MS has never connectedto previously, the mobile communication device 110 determines whetherthe signal quality of the new non-cellular network is greater than athreshold value (step S670). If so, the flow proceeds to step S640, andif not, the flow goes back to the initial state.

It is noted that, before performing the smart handover method of FIG. 6,the mobile communication device 110 may first perform a 2-stagemonitoring of the signal quality of any nearby non-cellular network, asshown in FIG. 7. In the first stage, the mobile communication device 110may periodically detect the signal quality of any nearby non-cellularnetwork during every N seconds, wherein N may be configured to be 6, 15,or any other number, depending on the power-saving settings of themobile communication device 110. Once the signal quality of anon-cellular network is detected to be greater than a first thresholdX1, then the mobile communication device 110 proceeds to the secondstage where it continues to monitor the signal quality of the detectednon-cellular network and detect its moving direction in relation to thedetected non-cellular network. When the signal quality of the detectednon-cellular network is greater than a second threshold X2 and it isdetected that the mobile communication device 110 is moving towards theAP of the detected non-cellular network, the mobile communication device110 may perform the smart handover method of FIG. 5, wherein the secondthreshold X2 is greater than the first threshold X1. Specifically, themoving direction of the mobile communication device 110 may bedetermined by calculating the moving average of the monitored signalquality of the non-cellular network. FIG. 8A is a schematic diagramillustrating RSSI changes for inward movement towards a non-cellularnetwork according to an embodiment of the invention. As shown in FIG.8A, the RSSIs of the detected non-cellular network monitored at time t1,t2, t3, t4, and t5 are −91 dBm, −88 dBm, −86 dBm, −90 dBm, −84 dBm,respectively, wherein the RSSI monitored at time t4 may be discarded asnoise. The moving average of the mobile communication device 110 may bedetermined by calculating the slope of the monitored RSSIs. Since theslope of the monitored RSSIs is positive, it is determined that themobile communication device 110 is moving towards the AP of the detectednon-cellular network. FIG. 8B is a schematic diagram illustrating RSSIchanges for outward movement from a non-cellular network according to anembodiment of the invention. As shown in FIG. 8B, the RSSIs of thedetected non-cellular network monitored at time t1, t2, t3, t4, and t5are −91 dBm, −88 dBm, −86 dBm, −88 dBm, −90 dBm, respectively, whereinthe RSSI monitored at time t3 may be considered as a turning point withrespect to the moving direction of the mobile communication device 110.The moving average of the mobile communication device 110 may bedetermined by calculating the slope of the monitored RSSIs. Since theslope of the monitored RSSIs is negative, it is determined that themobile communication device 110 is moving away from the AP of thedetected non-cellular network. In another embodiment, the Simple MovingAverage (SMA) formula may be employed for determining the movingdirection of the mobile communication device 110, and the invention isnot limited thereto. Note that the detailed descriptions concerning thecalculation of the SMA are omitted herein as they are beyond the scopeof the invention.

FIG. 9 is a flow chart illustrating a smart handover method for handingover the mobile communication device 110 from the non-cellular network130 to the cellular network 120 according to an embodiment of theinvention. In this embodiment, the mobile communication device 110 isinitially connected to the non-cellular network 130 and is in a“WiFi-associated” state. To begin, the mobile communication device 110periodically determines whether the speed of the link to the AP 131 islower than 2 Mbps and whether the signal quality of the non-cellularnetwork 130 is lower than a threshold T (step S910). Specifically, thespeed of the link to the AP 131 may be determined according to thetransceiving status between the mobile communication device 110 and theAP 131, and the threshold T is used to eliminate the situation where themobile communication device 110 may be moving at a high speed away fromthe AP 131 and used to eliminate the situation where the detected speedof the link to the AP 131 may not be accurate for real-time changes. Forexample, the speed of the link to the AP 131 detected at time t1 isgreater than 2 Mbps and the next periodic detection is 6 secondsthereafter. In this example, the mobile communication device 110 movesrapidly away from the AP 131 to a place where the signal quality of thenon-cellular network 130 drops sharply in less than 6 seconds. Note thatthe speed of the link to the AP 131 detected at time t1 is not accurateenough to be taken as the only measuring factor. Accordingly, thethreshold T is used. The value of the threshold T may be predeterminedto be a specific number according to any one or more considerations,such as the coverage of the non-cellular network 130, the geologicalenvironment of the non-cellular network 130, etc. Note that, the lowerbound for the speed of the link to the AP 131 may be configured to anyvalue other than 2 Mbps, and the invention is not limited thereto.

Subsequent to step S910, if so, the mobile communication device 110further determines whether a link to the cellular network 120 isavailable and whether the speed of the link to the cellular network 120is greater than the speed of a GPRS link (step S920). Specifically, themobile communication device 110 may first perform an attachmentprocedure to register to the cellular network 130, and a link to thecellular network 120 is available if the registration is successful. Thespeed of the link to the cellular network 120 may be determinedaccording to the system information broadcasted by the cellular network120, and in general, the speed of a GPRS link is up to 80 Kbps fordownlink and 20Kbps for uplink with Coding Scheme 4 (CS-4). In anotherembodiment, if the type of wireless service in use requires a higherdata rate, the mobile communication device 110 may instead determine, instep S920, whether the speed of the link to the cellular network 120 isgreater than (or equal to) the speed of a WCDMA link, an HSPA link, oran LTE link.

If a link to the cellular network 120 is available and the speed of thelink is greater than the speed of a GPRS link, then the mobilecommunication device 110 conducts handover from the non-cellular network130 to the cellular network 120 (step S930), and then disconnects withthe non-cellular network 130 and enters the “Cellular-connected” state.In another embodiment, before step S930, the mobile communication device110 may prompt the user to confirm whether to proceed to performhandover from the non-cellular network 130 to the cellular network 120,and only proceed to step S930 when the user confirms the decision.Subsequent to steps S910 and S920, if not, the mobile communicationdevice 110 stays in the “WiFi-associated” state and waits for the nextperiodic check on the speed of the link to the AP 131.

It is noted that, before performing the smart handover method of FIG. 9,the mobile communication device 110 may first perform a 2-stagemonitoring of the signal quality of any nearby non-cellular network, asshown in FIG. 10. In the first stage, the mobile communication device110 may periodically detect the signal quality of the non-cellularnetwork 130 in every N seconds, wherein N may be configured to be 6, 15,or any other number, depending on the power-saving settings of themobile communication device 110. If once the signal quality of thenon-cellular network 130 is detected to be lower than a first thresholdY1, then the mobile communication device 110 proceeds to the secondstage where it continues to monitor the signal quality of thenon-cellular network 130 and detect its moving direction against thenon-cellular network 130. When the signal quality of the non-cellularnetwork 130 is lower than a second threshold Y2 and it is detected thatthe mobile communication device 110 is moving away from the AP 131, themobile communication device 110 may perform the smart handover method ofFIG. 9, wherein the first threshold Y1 is greater than the secondthreshold Y2. Specifically, the moving direction of the mobilecommunication device 110 may be determined by calculating the movingaverage of the monitored signal quality of the non-cellular network 130.For the calculation of the moving average, reference may be made to therelated descriptions of FIGS. 8A and 8B.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. Those who are skilled in this technology can still makevarious alterations and modifications without departing from the scopeand spirit of this invention.

Use of ordinal terms such as “first”, “second”, “third”, etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

1. A mobile communication device, comprising: a first processing logicunit configured to connect the mobile communication device to a firstwireless network for wireless transceiving via a first link; a secondprocessing logic unit configured to determine whether a second link to asecond wireless network is available in response to detecting a lowperformance condition of the first link, wherein the first wirelessnetwork and the second wireless network are heterogeneous networks; anda third processing logic unit configured to hand over the mobilecommunication device from the first wireless network to the secondwireless network in response to a transceiving rate of the second linkbeing greater than a first value.
 2. The mobile communication device ofclaim 1, wherein the low performance condition of the first link isobtained according to a transceiving rate of the first link or a signalquality of the first wireless network.
 3. The mobile communicationdevice of claim 2, wherein the low performance condition of the firstlink indicates that the transceiving rate of the first link is lowerthan a second value or the signal quality of the first wireless networkis lower than a predetermined threshold.
 4. The mobile communicationdevice of claim 1, wherein the first wireless network is a non-cellularnetwork and the second wireless network is a cellular network.
 5. Themobile communication device of claim 4, wherein the non-cellular networkis a Wireless Local Area Network (WLAN), Bluetooth Personal Area Network(BT PAN), or ZigBee Wireless PAN (ZigBee WPAN).
 6. A method for a mobilecommunication device to handover between a plurality of heterogeneousnetworks, comprising: connecting to a first wireless network forwireless transceiving via a first link; determining whether a secondlink to a second wireless network is available in response to detectinga low performance condition of the first link, wherein the firstwireless network and the second wireless network are heterogeneousnetworks; and handing over the mobile communication device from thefirst wireless network to the second wireless network in response to atransceiving rate of the second link being greater than a first value.7. The method of claim 6, wherein the low performance condition of thefirst link is detected according to a transceiving rate of the firstlink or a signal quality of the first wireless network.
 8. The method ofclaim 7, wherein the low performance condition of the first linkindicates that the transceiving rate of the first link is lower than asecond value or the signal quality of the first wireless network islower than a predetermined threshold.
 9. The method of claim 6, whereinthe first wireless network is a non-cellular network and the secondwireless network is a cellular network.
 10. The method of claim 9,wherein the non-cellular network is a Wireless Local Area Network(WLAN), Bluetooth Personal Area Network (BT PAN), or ZigBee Wireless PAN(ZigBee WPAN).
 11. A mobile communication device, comprising: a firstprocessing logic unit configured to connect the mobile communicationdevice to a first wireless network for wireless transceiving via a firstlink; a second processing logic unit configured to scan for a nearbysecond wireless network with a current signal quality, wherein the firstwireless network and the second wireless network are heterogeneousnetworks; a third processing logic unit configured to apply a conditioncheck on the current signal quality of the second wireless networkaccording to a result of whether the mobile communication device waspreviously connected to the second wireless network prior to beingconnected to the first wireless network; and a fourth processing logicunit configured to hand over the mobile communication device from thefirst wireless network to the second wireless network in response topassing of the condition check.
 12. The mobile communication device ofclaim 11, wherein the step of handing over the mobile communicationdevice further comprises: connecting to the second wireless network viaa second link; and disconnecting with the first wireless network. 13.The mobile communication device of claim 11, wherein the condition checkcomprises: determining whether the current signal quality of the secondwireless network is greater than a predetermined threshold, if themobile communication device was not previously connected to the secondwireless network prior to being connected to the first wireless network;and determining whether the current signal quality of the secondwireless network is greater than the sum of a previous signal quality ofthe second wireless network, which was obtained when the mobilecommunication device was previously connected to the second wirelessnetwork prior to being connected to the first wireless network, and amargin value for eliminating a ping-pong effect.
 14. The mobilecommunication device of claim 11, wherein the first wireless network isa cellular network and the second wireless network is a non-cellularnetwork.
 15. The mobile communication device of claim 14, wherein thenon-cellular network is a Wireless Local Area Network (WLAN), BluetoothPersonal Area Network (BT PAN), or ZigBee Wireless PAN (ZigBee WPAN).16. A method for a mobile communication device to handover between aplurality of heterogeneous networks, comprising: connecting to a firstwireless network for wireless transceiving via a first link; scanningfor a nearby second wireless network with a current signal quality,wherein the first wireless network and the second wireless network areheterogeneous networks; applying a condition check on the current signalquality of the second wireless network according to a result of whetherthe mobile communication device was previously connected to the secondwireless network prior to being connected to the first wireless network;and handing over the mobile communication device from the first wirelessnetwork to the second wireless network in response to passing of thecondition check.
 17. The method of claim 16, wherein the step of handingover the mobile communication device further comprises: connecting tothe second wireless network via a second link; and disconnecting withthe first wireless network.
 18. The method of claim 16, wherein thecondition check comprises: determining whether the current signalquality of the second wireless network is greater than a predeterminedthreshold, if the mobile communication device was not previouslyconnected to the second wireless network prior to being connected to thefirst wireless network; and determining whether the current signalquality of the second wireless network is greater than the sum of aprevious signal quality of the second wireless network, which wasobtained when the mobile communication device was previously connectedto the second wireless network prior to being connected to the firstwireless network, and a margin value for eliminating a ping-pong effect.19. The method of claim 16, wherein the first wireless network is acellular network and the second wireless network is a non-cellularnetwork.
 20. The method of claim 19, wherein the non-cellular network isa Wireless Local Area Network (WLAN), Bluetooth Personal Area Network(BT PAN), or ZigBee Wireless PAN (ZigBee WPAN).